Microtubules are highly dynamic cellular structures involved in a multitude of cellular functions including cell secretion, membrane bound ligand mobility and the movement of chromosomes in mitosis. In the cytoplasm the equilibrium between polymer and subunits may involve a complex and highly regulated behavior. There is a constant subunit flow from one end of the microtubule to the other. This flow potentially creates the machinery for movement of attached organelles, such as chromosomes, as a consequence of maintaining the equilibrium. In vitro, this flow, or "treadmilling" is regulated by a cAMP dependent kinase which phosphorylates a microtubule associated protein. We propose: (1) to study the co-variance of different assembly parameters including rate and efficiency of treadmilling, with distinct microtubule related kinase activities; (2) to isolate and characterize microtubule associated phosphatase and adenylate cyclase activities that may play a role in the overall kinase dependent control mechanism; (3) to determine if treadmilling occurs in the cell and, if so, how its rate and efficiency may vary with kinase activity, and lastly; (4) to determine if the avian sarcoma protein, (apparently linked to cell transformation) pp60src, alters microtubule behavior in vitro and in vivo through a cAMP independent kinase activity.